const PENDING = "pending";
const FULFILLED = "fulfilled";
const REJECTED = "rejected";

class MyPromise {
  static all(array) {
    let result = [];
    let index = 0;
    return new MyPromise((resolve, reject) => {
      function addData(i, value) {
        result[i] = value;
        index++;
        if (index === array.length) {
          resolve(result);
        }
      }
      for (let i = 0; i < array.length; i++) {
        let current = array[i];
        if (current instanceof MyPromise) {
          //promise对象
          current.then(
            (value) => addData(i, value),
            (reason) => reject(reason)
          );
        } else {
          //普通值
          addData(i, array[i]);
        }
      }
      // resolve(result);
    });
  }
  static race(arr) {
    return new MyPromise((resolve, reject) => {
      for (let i = 0; i < arr.length; i++) {
        let current = arr[i];
        if (current instanceof MyPromise) {
          current.then(
            //直接执行，状态不可修改
            (value) => resolve(value),
            (reason) => reject(reason)
          );
        } else {
          resolve(current);
        }
      }
    });
  }
  static resolve(value) {
    if (value instanceof MyPromise) return value;
    return new MyPromise((resolve) => resolve(value));
  }
  constructor(executor) {
    try {
      executor(this.resolve, this.reject);
    } catch (e) {
      this.reject(e);
    }
  }
  //promise状态
  status = PENDING;
  //成功之后的值
  value = undefined;
  // 失败后的原因
  reason = undefined;
  //成功回调
  successCallback = [];
  //失败回调
  failCallback = [];
  resolve = (value) => {
    //如果状态不是PENDING 阻止程序向下执行
    if (this.status !== PENDING) return;
    //将状态改为成功
    this.status = FULFILLED;
    //保存成功之后的值
    this.value = value;
    //判断成功回调是否存在 如果存在就调用
    // this.successCallback && this.successCallback(this.value);
    while (this.successCallback.length) this.successCallback.shift()();
  };
  reject = (reason) => {
    //如果状态不是PENDING 阻止程序向下执行
    if (this.status !== PENDING) return;
    //将状态改为失败
    this.status = REJECTED;
    //保存失败的原因
    this.reason = reason;
    //判断失败回调是否存在 如果存在就调用
    // this.failCallback && this.failCallback(this.reason);
    while (this.failCallback.length) this.failCallback.shift()();
  };
  then(successCallback, failCallback) {
    successCallback = successCallback ? successCallback : (value) => value;
    failCallback = failCallback
      ? failCallback
      : (reason) => {
          throw reason;
        };
    let promise2 = new Promise((resolve, reject) => {
      //判断状态
      if (this.status === FULFILLED) {
        setTimeout(() => {
          //用异步拿到promise2
          try {
            let x = successCallback(this.value);
            // resolve(x);
            // 判断x是普通值还是promise对象
            // 如果是普通值直接调用resolve
            // 如果是promise对象 则看promise对象返回的结果
            // 再根据promise返回的结果 决定调用resolve还是reject
            reslovePromise(promise2, x, resolve, reject); //用异步拿到promise2
          } catch (e) {
            reject(e);
          }
        }, 0);
      } else if (this.status === REJECTED) {
        setTimeout(() => {
          try {
            let x = failCallback(this.reason);
            reslovePromise(promise2, x, resolve, reject);
          } catch (e) {
            reject(e);
          }
        }, 0);
      } else {
        //等待
        //将成功回调和失败回调存储起来
        this.successCallback.push(() => {
          setTimeout(() => {
            try {
              let x = successCallback(this.value);
              reslovePromise(promise2, x, resolve, reject);
            } catch (e) {
              reject(e);
            }
          }, 0);
        });
        this.failCallback.push(() => {
          setTimeout(() => {
            try {
              let x = failCallback(this.reason);
              reslovePromise(promise2, x, resolve, reject);
            } catch (e) {
              reject(e);
            }
          }, 0);
        });
      }
    });
    return promise2;
  }
  finally(callback) {
    return this.then(
      (value) => {
        return MyPromise.resolve(callback()).then(() => value);
        // callback();
        // return value;
      },
      (reason) => {
        // callback();
        // throw reason;
        return MyPromise.resolve(callback()).then(() => {
          throw reason;
        });
      }
    );
  }
  catch(failCallback) {
    return this.then(undefined, failCallback);
  }
}

function reslovePromise(promise2, x, resolve, reject) {
  if (promise2 === x) {
    return reject(new TypeError("Chaining cycle detected for promise"));
  }
  if (x instanceof MyPromise) {
    //是一个promise
    // x.then((value) => resolve(value),(reason) => reject(reason));
    x.then(resolve, reject);
  } else {
    //普通值
    resolve(x);
  }
}

module.exports = MyPromise;
